How long does the buffer holds the data?

[Former Member]

Hi guys,

How long does the buffer holds the data?

Let's say I run this report now then after 2 seconds I again run the report with the same data but now it takes much lesser time to execute. After 1 hour, it goes back to its original runtime which is slower.

How do we know that the data is still in the buffer or not? Are basis people know more about this?

Please advice.

Thanks!

[Former Member]

There will probably be more than one buffer involved and yes, basis experts probably know more about this than ABAPers.

Rob

[Former Member]

Hello,

The SAP application uses different buffers.

First of all the SAP buffers, containing programs, screens, some table data, number ranges, ...

For most of these buffers SAP uses LRU displacement, meaning Least Recently Used.

Buffers in SAP have a certain size (can be set by BC administrators) and therefor can only contain a certain amount of data.

Objects that are not used for a long time are first displaced, this means that the buffers contains only recently used objects; that's the LRU displacement.

Putting an exact time on this is very difficult, this depends on the size of the buffers, number of users, number of objects that need to be displaced, ...

You can view the SAP buffers via ST02 and also the objects that are currently in the buffers.

Via ST02 you can also see the number of displacements and quality.

SAP also uses the database buffers.

This is why the second time you run a report it goes much faster.

Database buffers store the most recently used blocks of data also via the LRU mechanism.

These buffers can be seen via ST04 and are most of the time much bigger then the SAP buffers.

Here again it is very difficult to say how long data stays in the buffers, this strongly depends on database size, number of users and of course size of the database buffers.

There exist some good SAP guidelines about buffer quality, this can be used as a reference to set the parameters in your system.

[http://help.sap.com/saphelp_nw04/helpdata/EN/c4/3a6ef3505211d189550000e829fbbd/content.htm|http://help.sap.com/saphelp_nw04/helpdata/EN/c4/3a6ef3505211d189550000e829fbbd/content.htm]

[http://help.sap.com/saphelp_nw04/helpdata/EN/c4/3a6ecc505211d189550000e829fbbd/content.htm|http://help.sap.com/saphelp_nw04/helpdata/EN/c4/3a6ecc505211d189550000e829fbbd/content.htm]

In case you use Oracle as database :

[http://help.sap.com/saphelp_nwpi71/helpdata/en/c4/3a71fc505211d189550000e829fbbd/content.htmhttp://help.sap.com/saphelp_nwpi71/helpdata/en/c4/3a71fc505211d189550000e829fbbd/content.htm|http://help.sap.com/saphelp_nwpi71/helpdata/en/c4/3a71fc505211d189550000e829fbbd/content.htm]

Wim